System for adjustment of transmission levels



ATTORNEY INVENTOR L-.. G. ABRAHAM SYSTEM FOR ADJUSTMENT OF TRANSMISSION LEVELS Filed Jan. 19, 1932 kmwSwkww Nov. 21, 1933.

Patented Nov. 21. 1933 I "PATENT OFFICE,

' SYSTEM FOR ADJUSTMENT OF TRANSMISSION LEVELS Leonard G. Abraham, Madison, N. J assignor to American Telephone and Telegraph Company, a corporation of New York Application January 19, 1932. Serial No. 587,592

14 Claims.

It is among the objects of myinvention to provide anew and improved method and correspondingapparatus for adjusting transmission on a signaling circuit. Another object of my invention'is'to provide for automatic adjustment of gain. at each of several repeaters in tandem on a long transmission line so as to preserve the proper energy level at each of these repeaters. Still another object of my invention is to'provide for making such adjustments very quickly, so as to interfere with the regular service of the line as little as practicable. Still another object is to provide for applying a current of a single frequency to a line-and separating it out at the re- 7 peaters and applying it according to its intensity at each repeater to make corresponding adjustments for gain in such repeaten All these objects and various other objects and advantages of my invention will become apparent on consideration of an example of practice according to the invention which I have chosen for disclosure in j the following specification. It will be understood that this specification relates principally to this particular example of the invention and that the scope of the invention will be indicated in the appended claims. a r H Referring to the drawing, Figure 1 is a diagram of atransmission line with equipment for the practice of my invention, and Fig. 2 is a diagram showing the apparatus associated with one of the repeaters.

A long transmission line 10' is indicated in Fig. 1 with the usual terminal apparatus 11 at its ends. The line 10-10 is a four-wire-line comprising a conductor pair 10 for transmission from west to east and a conductor pair 10' for transmission from east to west. interposed along each of these pairs 10 and 10 there are one-way repeaters 23 in tandem and'at certain of these repeaters, such as 23', there is extra equipment for automatic adjustment of gain as shown more in detail in Fig. 2. For example, the repeaters might be fifty miles apart and the special equipment mentioned might be provided at.

' every tenth repeater, i. e., at stations five hundred miles apart, assuming a line say four thousand miles long.

At each repeater such as 23' shown in Fig. 2,

there is an adjusting pad, i. e., an adjustable loss network comprising steps of series resistance 24 and 24 and steps of shunt resistance 25, which may be cut in or out by the relay contacts 31, 31 and 32 controlled by the relays 33. It will be noticed that these relays 33 are numbered from 0 to 6 and like numbers are found on the relay contacts 31, 31 and 32. These numbers mean that each relay operates the like numbered contacts. Thus, in the state of affairs shown in Fig. 2, the only one ofthe seven relays 33, individually numbered 0 to 6, that is operated 'at this time is No. 2, and it will be seen that only the No. 2 contacts are operated in the groups of contacts 31, 32 and 32. Thus at this time there are two stages of series resistance units 24, 24 in the line and five stages of shunt resistances connected across the line. In other words there are now two stages or units of loss in the line.

The operated condition of relay No. 2 of the relays 33 is readily established by tracing the circuit from ground G10 through battery B3, the particular relay No. 2, the segment No. 2 of dial D2, the corresponding dial index and ground Gs.

This corresponds to the assumption that at the last preceding operation to make adjustment, the proper condition was found at the adjustment that has just been described with the arm of dial D2 on its segment No. 2. e

Let it be assumed that the repeater shown in Fig; 2 is the first in order of the repeaters 23 proceeding in the direction of the transmission from the transmitting end of the conductor pair in which this repeater 23' is interposed. Further features of construction of the system shown in Fig. 2 will readily be apprehended from the following description of a normal operation for adjustment.

' The operator at the sending end of the line 10, desiring to make the adjustments provided by this'system, shifts the switches 34 (see Fig. .1) for a brief period of time of the order of two or three seconds, thus putting the 900 cycle oscillator 35 across the line 10 at its input end. This 900 cycle current from the generator 35 has a definite energy intensity and; of course, like the various components of voice currents, it is at-, tenuated along the successive stretches of line between the repeaters and amplified to compensate at each repeater. This 900 cycle current flows through the first specially equipped repeater 23 and enters the selective circuit 36 which is connected across the line on the output side of the repeater 23'. This selective circuit 36 passes the 900 cycle current to the input of the detector 37 and the corresponding output current'from the detector 37 goes through the relays R1 and R2 in series. The relayRi will operate and open the circuit of relay R3. But because of the condenser C and the resistances T2 and T3, the relay R3 will be slow-acting and will release its armatures only after a time interval of say 0.05 second. Relay R2 may or may not operate according to the current intensity on the output side of repeater 23', as will be considered presently.

It should be noticed that of course normal voice currents on the line will comprise components of the samespecial frequency 900 cycles, and when these are present they will be. passed by the selective circuit 36 to the detector 3'7 and they may operate the relay-R1, as has just been applying the 900 cycle current at the sending end. .But assuming that the intended 900 cycle testing current has been applied-by closure of the switches 34 and that the relay R1 hasbeen oper ated and relay R2 has released, as described heretofore, then a circuit will be closed as follows: from ground G2 to the back contact of relay R3, back contact of relay Rs, winding of relay 28, battery 29 and ground 30.v The resulting operation of the relay 28 will cut in a loss network or pad of about 6 decibels comprising the. series-resistances 26 and the shunt'resistance. 27. While this loss pad remains in the circuit it will attenuate the 900 cycle current going on fromthe repeater 23 so that it will-be of low intensity at the next repeater 23 equipped with such appar'atus; the effect at such next repeater will be discussed presently. If the level on theoutput side of the repeater 23 is too low the relay R2 will not operate, and if this level is too high the relay R2 will operate. Accordingly there are two cases to be considered. The proper point of discrimination is secured by adjustment of the detector 37, particularly of the battery in its input circuit. 7

Case'1.--Assuming that theltransmission level on the output sideof the repeater 23? is high, and accordingly the relay R2 will be operated when relay R3 releases, the operation of relay R2 will close a circuit as follows: from ground Gr, through battery' B2; relay winding R4, front contact of relay R2 and ground. Relay R4 will lock itself up through the circuit from ground G1, battery B2, winding of relay R4, front.- contact of this relay,,back contact of relay R3 and ground G2. The slow-operating relay Rs will tend to operate through-thecircuit from ground G10, battery B3, winding of relay Re, back contact of relay R3 and ground G2. But because of its slow-operating character, the relay Rs will not operate until a certain time interval has elapsed.

Also,-.the operationof the relay R2 and the release of the relay R2 close a circuit for the stepping selector SX'as follows: from, ground Ge, through battery B1, the, winding of this selector, backcontact of relay R7, back contact of relay Ra, front contact of relay R2-to groundGs. The selector Sx beginsto step the arms of dials Di'and D2 around clockwise, and accordingly the arm of dial D2 opensthe circuit of No.2 relay inthe relay set 33 and closes the circuit through-relay No. 3 of the. same set, thus introducing an additional stepv of loss in the adjusting .pad

3l-3132. This increased loss on the input side of the repeater 23 leads to a reduction of intensity in the output circuit of the detector 3'7 and if it brings the intensity down to the proper level on the output side of the repeater 23 the relay R2 will release. But if this level is notbrought down to theproper point, the relay R2 will not release and the arm of dial D2 will step along from segment to segment, successively releasing the operated relays of the set 33 and operating those next in order and introducing more and more loss in. steps in the pad 3l3l'32. Whenever the resultant decrease of intensity on the output side of the repeater 23 is such that the proper power level is attained, then the relay R2 releases, opening the circuit for the selector 8x and stopping the selector so as to preserve the corresponding adjustment of the pad 3l3l32. When the relay R4 is operated, as described above, it closes a circuit that operates the relay R5 asfollows: from ground G4, through battery B2, Winding of said relay R5, front contact of relay R4, segment No. 2 of dial D1, the arm of this dial to ground G7. This relay R5 will be operated likewise, whatever segment the arm of dial Dyengagesexcept the segment designated 0' (unless relay Rs' is already operated when the segment is No. 6). a s

- Assuming thatthe introduction of loss-on the input side of the repeater 23 proceeds so far that the decrease of intensity on the output side causes the relay R2 to release while the arms of dials D1 and D2 are on a segment 3, .4 or 5, and that as described above the selector Sx has stopped atthatadjustment, then presently the slow-operating relay R5 will operate through the circuit traced heretofore. Its operation will open the circuit for the relay 23 and cut out the loss pad 26-27 from the line on the output side of the repeater 23",.thus increasing the intensity of the 900 cycle currentgoing to the second repeater 23'. The eiT ect there will be considered presently.

If-the dials D1 and D2 are stepped along to their segments 6, this will close the circuit through relay No. 6 of the relay set 33, but this particular circuit includes the winding R2 on the slow-operating relay Rs-Rg and the operation of this relay closes an alarm circuit. The consequent alarm' is justified for it is due to the fact that cutting in all the available steps of loss in the pad 31-31 is insufiicient or barely sufiicient to bring the transmission level down to the proper adjustment and personal attention is required.

'If the two arms of the dials D1 and D2 are stopped so far along that they reach their respective No. 6 segments, there are two sub-cases to be considered, namely, when relay R2 releases at this stage and when it does not release at this stage. In either sub-case the arms of the dials D1 and D2 will bearrested on their respective No. fi segments, as will be'explained presently.

'It may be that although the amount of loss introduced on the input side of the repeater 23 at the fifth stage of the dials was not enough, yet'the, total amount of loss which will be introduced on the No. 6 segment will be enough. This 'sufiiciency will be signified by the release 1 of the relay R2 in the plate circuit of the detector not sufficient to bring the system down to the "of the selector S2 at the relay R7.

No. 6 will close the circuit of relay R7 from ground G4, through battery B2, winding of relay R1, front contact of relayRs, segment No.6, arm of dial D1 to ground Gv, and this will open the circuit Whether or not the relay R2 releases when the dial arms D1 and D2 reach their No. 6 segments, in either of these two sub-cases the slow operating relay RS whose'circuit was closed at relay R; will presently operate. The operation of the relayRs deenergizes relay 28 thus' cutting out the loss pad 26- -27 and permitting the current of 900 cycle frequency to go without reduced strength on to the next similar repeater 23".

Case 2.Returning to the state of affairs just after the relay R; has released" due to sustained current at 900 cycle frequency applied to the detector 3' 7, let us suppose that this current is of low intensity not suflicient to energize the relay R2 in the output circuit of the detector 37. The release of the relay R3, just mentioned, will put current through the slow-operating relay Rs, but before it operates the stepping selector S2 will receive current through the circuit traced from groundGe, through battery B4, selector Sx, back contact of relay Rv, back contact of relay R3, back contact of relay R4, segment 2 of dial D1 to ground G Accordingly,.the selector S2 will step the dial arms at D1 and D2 along and will continue to receive current'by a circuit completed through one or another of the various segments of the dial Druntil its arm leaves the No. 6 segment; then the said circuit will be broken and thejselector 8;; will stop withthe dial arms on the 0 segments. Thereupon, relay R4 will receive current over, the following circuit: from ground G4, through battery B2, winding of relay R1, segment 0' of dial D1 to ground G1. Withthe arm of dial D1 on the 0 segment, the arm of dial D2 will be on its 0 segment and the. 0 relay of the relay set 33 will be operated and all loss will be cut out of the pad 313l 2. If the relay R2 does notoperate under these circumstaziceathat is, with no reduction of gain on the input side of the repeater, then the se lector Sx will stay on the 0 segment and the slow-operating relay RaR9 will close its circuit and give an alarm. In this case the alarm will be given because the extremeadjustment of cutting. out loss fails to bring the level up to the proper value. Also, at this stage, slow-operating relay R6 will operate and remove, theloss pad 26-27 and permit'the 900 cycle current to go on to the next repeater to operate its adjuster.

On the other hand, when the dial arms reach the 0 segments, this removal offlall loss on the input. side of the repeater 23" may permit the current intensity on the output side of this repeater to rise .high enough tooperate through the detector 3'7 to energize the relay 1 2.2, .In this case the system will operate starting from the 0 segments of the dials D1 and D2 in the same manner that has been described heretofore in Case 1, starting. from the No. 2 segments of the dials Drand D2, andin the present case the adjustment will be reached on some segmentpresumably nearer to the 0 segment than the segment from which the dial arm started. a The description of 'a cycle of operation that has been given in the foregoing cases-1 and 2,

has been for the firstrepeater'in the tandem row of repeaters beginning at thetransmission end of the line. In both these cases'and their subcases, the relay R: by its release cuts in the pad 26-27, the operation of the dials D1 and D2 by the stepping selector follows, and then the slow operating relay Re cuts out the pad. At the second repeater 23, the situation will be somewhat' different from that at the first repeater 23'. When the loss pad 26--27 wasintroduced at this first repeater it meant that a 900 cycle current got through to'the second repeater, but with low intensity. Therefore, at this time the adjuster at the second repeater will go to its 0 3 point in just the same manner that has been described for the first repeater in case thepower level is too low. Thus, while the first repeater is being adjusted the second repeater is getting ready for adjustment by having its adjuster stepped along to the' 0 segments onits dials.

repeater when the associated loss'pad 26-27 is removed, the 900 cycle currentgoes on at the proper power level and the adjuster at the second repeater adjusts from 0 loss on its input side up to the proper degree of loss to give the proper power level on its output side; provided, of course, that there is not an extreme condition at the second repeater, which would lead to the giving of an alarm there, just as has been described for thealarm at the first repeater conline 4,000 miles long with 20,000 milesper sec.- ond velocity. The time of transmission over this circuit may properly be assumed to be about 0.2 second. Also assuming adjusters at 500 mileintervals, there will be eight adjusters and if each requires 0.2 second this willbe 1.6 seconds-for Then at the close of the adjustment of the first all of them and adding in the 0.2 second for the time on the line, the total time will be 1.8 seconds. Thus, just previous to make connections for conversation on a circuit, the adjustment for level all along its length can be effected within a period of 2 seconds. 2.

If ringing is practiced over the circuit and if 1000 cycles per second current is employed for ringing, the choice of 900 cycles per second will assurethat the ringing current will not affect the level adjusters and reciprocally the level adjusting current will not affect the ringers. The selective circuits at the adjusters may be madefor 1000 cycles, that is, for the same frequency as the ringers. Inthis case the adjustment for power ff:

trolled dire'ctly by the correspondingringer. In

this case these relays will be omitted.

In so far as the adjuster at one repeater may fail to bring the power level to the proper value I at that point, the entire system will tend .to make correction by compensating adjustment at the next following adjuster, that'is, if the current goes oneastffrom the repeater in Fig. 2 at too high a level, then the adjuster on the input side of the next repeater to theeast will cut down the input to that repeater so as to have the proper level on its output side. Similarly if, after adjustment, the level is too low on the output side of the repeater 23 shown in Fig. 2, then at the next repeater to the east loss will be'cut out on its input side until the level is brought up to the proper value on the output side of that repeater.

The foregoing disclosure has related principally to a system in which the controlling current is applied on convenient occasions when signal currents are not being transmitted. At each such applicationthe apparatus will adjust itself and thereafter it will hold this adjustment until the controllingcurrent is applied again. 1 c

But by choosing a frequency for the controlling current lying outside the signal current range, this controlling" current may be applied continuously, so that theyapparatus will adjust itself at once whenever there is anysubstantial change of transmission loss,

Iclaim:

1. The method of adjusting tandem repeaters for gain in a line comprising those-repeaters which consists in sending a transient special frequency current over the line, selectively separating it out ateach of those repeaters, detecting this current and applying it to adjust the gain of the respective repeater according to its inten-,

, peaters, meanwhile introducing substantial loss beyond the point' at which the special current is diverted, detecting this current at the place Where it is separated out, applying it to adjust thegain of the respectiverepeater, and meanwhile applying the current of reduced intensity at the next following repater due to the interposition of said loss to operate its adjuster to make it ready for, adjustment when the said loss is removed upon the completion of adjustment at the first repeater.

4. In combination, a transmission line, tandem repeaters therein, a selective circuit connected across the line on the output side of each a repeater, a loss pad adapted for connection in theline just beyond the point of connection of said selective circuit, a marginal detector associated with each selective circuit, an adjustable pad on the input side of each repeater, and means to adjust such pad controlled by the corresponding detector.

5. In combination, a transmission line, a repeater therein, aselective circuit connected across the line on the output side of said repeater, a marginal detector associated with said selective circuit, a pad adjustable in steps on the input side of said repeater, a stepping selector toiintroduce said loss in steps from 0 up to the'greatest loss which the pad will give, and meanscontrolled by said detector to control the selector toincrease the steps to the proper adjustment when the method of adjusting for transmission beyond the point of connectionof said-selective circuit, a marginal detector associated with each selective circuit, an adjustable pad oncthe input side of each repeater, to adjust such pad controlled by the corresponding detector, and means to interpose said loss pad during adjustment of said adjustable pad.

7. A telephone line. having a repeater station thereon, control means governedv by a tone having a frequency within the voice frequency range transmitted at intervals over the line for controlling the gain to hold the energy level beyond the repeater within desired limits, and means for preventing operation of said control means by the voice currents transmitted during communication overthe line, 7

8. A communication line having a repeater station thereon, control means governed by a tone having a frequency within the voicefrequency range transmitted at intervals over the line for controlling the gain tohold the energy level beyond the repeater. within desired limits, and meanscomprising a slow acting relay for preventing operation of said control means by the voice currents during communication over the line. a j

'9. A communication line having a repeater station thereon, a potentiometer connected to said line before the repeater for controlling the, gain eiiected bythe repeater, apparatus foroperating said potentiometer, control means-governed bya tone having a frequencywithin the voice frequency range transmitted over said line and con nected to the line-beyond the repeater for controlling the gain of said apparatus to hold the energy level beyondthe repeater within a desired range, and means comprising a'slow acting relay for preventing operation of the control means by the voice currents during. communication over theline. w 7,

19', A communication line having a repeater station thereon,ra potentiometer comiected to said cline before the repeater for controlling the gain effected-thereby, control means connected to the line beyond the repeater and operated according to the energy level of atone having a frequency within the voice frequency range impressed on the line at intervals for governing'said potentiom eter to hold the energy level on the line within a desired ener y range, and'means for delaying the operation of said control means to prevent operation thereof to change the potentiometer setting by the voice currents during communication over the line. I

- 11. A telephone transmission line having a repeater station thereon, means controlled by a tone having a frequency within the voice frequency range transmitted over the line and amplified by thesame apparatus'which amplifies the voice currents for holding the energy level on'the line beyond the repeater within predetermined narrow limits when the energy variation' on the line at the startof theitransmission of the tone is within certain fixed limits, and means for operating analarrn only whenthe energy variations on the line at the start of, the'transmission of the tone are beyond said fixed limits.

1 12 A telephone transmission line having a re-' peater station thereon, means controlled by a tone having a frequency within the voice frequency range transmitted at intervals over the line and amplified by the same apparatus which amplifies the voice currents for holding the energy level on the line beyond the repeater within predetermined narrow limits when the energy variations on the line at the start of the transmission of the tone are within certain fixed limits, and means controlled by said tone for operating an alarm only when the energy variations on the line at the start of the transmission of the tone are beyond said fixed limits.

13. A telephone line for transmitting currents having frequencies within the voice frequency range, a repeater station on said line, and control means at the repeater station for governing the gain efiected by the repeater and controlled by a tone transmitted over the line, said tone being amplified by the same apparatus which amplifies the voice currents.

14. A signal transmission line for transmitting currents having frequencies within the voice frequency range, a repeater station on said line, and means controlled by a tone transmitted over the line for holding the energy level on the line beyond the repeater within predetermined limits, said tone being amplified by the same apparatus which amplifies the signaling currents.

' LEONARD G. ABRAHAM. 

